CHAPTER 11: SEXUAL REPRODUCTION AND MEIOSIS
WHERE DOES IT ALL FIT IN?
Chapter 11 continues the coverage of cell reproduction covered in Chapter 10 by applying the
concepts to sexual reproduction. Students are likely to confuse the events and details of mitosis
and meiosis. It is important to reinforce to students the differences and similarities of asexual and
sexual cellular division. Students should also be told upfront the goals and outcomes of meiosis
before proceeding with detailed coverage of Chapter 11. Chapter 10 should be regularly referenced
to help reinforce the principles of Chapter 12.
SYNOPSIS
Meiosis and syngamy constitute a cycle of sexual reproduction. Fertilization would double the
chromosome number of each subsequent generation except that the gametes possess only a
haploid complement of DNA. Thus the resultant zygote inherits genetic material from both its
father and its mother, in the case of humans, twenty-three chromosomes from each. Sexual
reproduction produces offspring that are genetically different from either parent while asexual
reproduction produces progeny that are genetically identical to the parent cell. The specific
events of sexual reproduction varies from kingdom to kingdom. For example, in most unicellular
eukaryotes, the individual cells function directly as gametes. In plants, specific haploid cells are
produced by meiosis, these cells then divide by mitosis to form a multicellular haploid phase
which further produces eggs and/or sperm. In animals special gamete-producing cells
differentiate from the other somatic cells early on in development. Only these cells are able to
undergo meiosis to create haploid eggs or sperm.
Gamete-producing cells differentiate from somatic cells early in development. While they
themselves are diploid, their products are haploid as a result of meiosis. Although meiosis and
mitosis share many features, including microtubule formation, meiosis is unique for three
reasons: synapsis, homologous recombination, and reduction division. During synapsis
homologous chromosomes physically pair along their length. In homologous recombination
genetic exchange, called crossing over, occurs between the homologues. Reduction division is
the two separate rounds of nuclear division that occur in the remainder of the process. In the first
division, homologous chromosomes pair, exchange material, and separate. No genetic replication
occurs before the second division when the non-identical sister chromatids separate into
individual gametes. Each division is composed of prophase, metaphase, anaphase, and telophase,
additionally labeled I or II.
Some of the most important events of meiosis occur during prophase I. The ends of the sister
chromatids attach to specific sites on the nuclear envelope. The attachment sites for the two
homologues are near one another ensuring that each chromosome associates closely with its
homologue. Each gene corresponds with its partner forming the synaptonemal complex. Certain
genes are exchanged between homologues, an event called crossing over. The homologues are
released from the membrane but remain tightly connected to one another. The homologues line
up along the central plate of the cell during metaphase I. Only one face of each centromere is
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accessible to microtubule attachment, thus each homologue attaches to only one polar spindle
fiber. The microtubules shorten at anaphase I and pull the homologues apart to opposite ends of
the cell. Each pole ends up with a complete set of haploid chromosomes. Telophase I finishes
division I, cytokinesis may or may not occur.
Meiosis II is essentially a mitotic process. During metaphase II, the still connected sister
chromatids line up along their new metaphase plate with spindle fibers from each pole attached
to each centromere. During anaphase II, the centromeres split and the sister chromatids are
drawn to opposite poles. The result is four cells containing a haploid complement of genetic
material.
Sexual reproduction is advantageous to species that benefit from genetic variability. However,
since evolution occurs because of changes in an individual’s DNA, crossing over and
chromosome segregation is likely to result in progeny that are less well-adapted than their
parents. On the other hand, asexual reproduction ensures the production of progeny as fit as the
parent since they are identical to the parent. Remember the adage, “if it’s not broken, don’t fix
it.” There are several hypotheses regarding the evolution of sexual reproduction. One is
associated with repairing double-stranded DNA breaks induced by radiation or chemicals. The
contagion hypothesis suggests that sex arose from infection by mobile genetic elements. The Red
Queen hypothesis theorizes that sex is needed to store certain recessive alleles in case they are
needed in the future. Along similar lines, eukaryotic cells build up large numbers of harmful
mutations. Sex, as explained by Miller’s rachet hypothesis, may simply be a way to reduce these
mutations. The “whole truth” is likely a combination of these factors. Regardless of how and why,
the great diversity of vertebrates and higher plants and their ability to adapt to the highly varied
habitats is indeed a result of their sexual reproduction.
LEARNING OUTCOMES
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Explain why both meiosis and syngamy are necessary for continued sexual reproduction.
Differentiate between haploid and diploid in terms of genetic composition and indicate whether
associated with somatic or gametic cells.
Discuss the three major features that differentiate meiosis and mitosis.
Identify the stages of meiosis I and the characteristic events of each stage.
Describe the characteristic events of each stage of meiosis II and indicate how these events
resemble mitosis.
Explain how the homologues are held together during prophase I.
Understand the genetic consequences of synaptonemal crossing over.
Describe how the spindle-fiber attachment to chromosomes differs between mitosis and meiosis.
Understand how and at what stage(s) chromosomes assort independently during meiosis.
Understand how sexual reproduction is different from asexual reproduction.
Indicate the evolutionary advantages and disadvantages of sexual reproduction and describe the
most current explanations for its development.
Understand the ultimate genetic and evolutionary consequences of meiosis and sexual
reproduction.
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COMMON STUDENT MISCONCEPTIONS
There is ample evidence in the educational literature that student misconceptions of information
will inhibit the learning of concepts related to the misinformation. The following concepts
covered in Chapter 11 are commonly the subject of student misconceptions. This information on
“bioliteracy” was collected from faculty and the science education literature.
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Students believe that sexual reproduction is merely for increasing populations
Students have trouble with the concept of somatic cells and germ cells
Students do not distinguish between the function of somatic and sex cells
Students commonly confuse the terms mitosis and meiosis
Students believe chromatin and chromosomes are identical in nature
Students believe the DNA is doubled only in mitosis and not in meiosis
Students believe that meiosis has an interphase II
Students are not able to accurately calculate chromosome number differences between
meiosis I and meiosis II
Students are confused by the terms “N” and “2N”
Students are confused when homologous chromosome separation occurs
Students are confused when chromatin separation occurs in meosis
Students cannot contrast between the terms fertilized egg and zygote
Students believe that only germ cells carry X and Y chromosomes
Students believe that only animals, and not plants carry out meiosis
Students believe that only higher plants carry out sexual reproduction
INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE
Meiosis is like roommates splitting up and dividing their belongings. The division is more
equitable if the towels are piled together and then divided up, the silverware piled together and
divided and so forth, than if things are arbitrarily thrown into one pile or another as they are
found. The first method ensures a more even distribution of items and is analogous to homologue
pairing.
Differentiating between mitosis and meiosis is like distinguishing between the production of cars
and trucks. Each uses the same machinery, but produces an entirely different product.
The evolution of reproduction adds a second step ahead of the first, like the evolution of PS II/PS
I photosynthesis. The second division of meiosis is equivalent to the single division of mitosis,
chromatids separate from one another. It is slightly different from mitosis in that the sister
chromatids are not identical. The first division of meiosis is a new event. The homologues pair,
form synaptonemal complexes, and then move to the metaphase plate.
Stress the importance of crossing over and the random assortment of homologues as they relate
to producing genetic variation. Meiosis results in (1) genetic variation and (2) the reduction of
the genetic complement in preparation for syngamy. It is part of the sexual reproductive process.
A thorough understanding of meiosis is necessary to grasp what occurs in Mendelian genetics. It
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is amazing that Mendel was able to formulate his ideas without knowledge of either mitosis or
meiosis.
HIGHER LEVEL ASSESSMENT
Higher level assessment measures a student’s ability to use terms and concepts learned from the
lecture and the textbook. A complete understanding of biology content provides students with
the tools to synthesize new hypotheses and knowledge using the facts they have learned. The
following table provides examples of assessing a student’s ability to apply, analyze, synthesize,
and evaluate information from Chapter 11.
Application
Analysis
Synthesis
Evaluation
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Have students describe the “day in a life of DNA” during a meiosis event.
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Have students explain which stage would be best to study chromosome
number and identity during meiosis.
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Ask students a major reason why children some children look more like
one parent why others appear to have a mixture of both parents.
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Ask students to compare and contrast mitosis with meiosis II.
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Ask students explain meiosis in an organism with a 4N complement of
DNA.
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Ask students explain why crops that have a 3N chromosome complement
do not produce viable seeds and pollen.
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Ask students predict the effects on reproduction if germ cells underwent
meiosis I without being following by meiosis II.
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Have students explain why offspring produced by two organisms with
two different chromosome amounts would have trouble producing germ
cells.
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Asks students determine the probable use of a chemical that inhibits the S
phase of interphase during meiosis.
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Ask students to benefits an athlete may derive by resting and eating
performance athletic event.
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Ask students explain the benefits of citrus plants that contain zygotes and
parthenogenetic offspring in the same seed.
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Have students evaluate the possible effects on humans of a pollutant the
increases the probability of chiasma formation.
VISUAL RESOURCES
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Faculty can utilize similar visuals as in mitosis, but with a distinction between homologues and a
resulting halving of the genetic complement.
Construct a model of the chiasmata as indicated in the text using two strands of thick yarn
representing the chromosomes and a ring representing the chiasmata.
IN-CLASS CONCEPTUAL DEMONSTRATIONS
A. “DNA in Motion”
Introduction
Role playing is a fun activity to do with students as a means of reinforcing the fate of
DNA during meiosis. This activity helps student’s visualize the events of meiosis. It particularly
focuses on the segregation and separation of DNA in the different phases of gamete formation.
Materials
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8 Student volunteers
4 XL white T-shirts with “maternal” written large on front and back in black ink.
o One shirt should also have Chromosome 1 written on the front and back
o One shirt should also have Chromosome 2 written on the front and back
4 XL white T-shirts with “paternal” written large on front and back in black ink.
o One shirt should also have Chromosome 1 written on the front and back
o One shirt should also have Chromosome 2 written on the front and back
4 sheets 8 ½“ by 11” pink paper
4 sheets 8 ½“ by 11” blue paper
8’ x 8’ section of floor marked with chalk or tape
Procedure & Inquiry
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Introduce the topic of meiosis and discuss the fate of the DNA.
Call 8 students to the front of the room and instruct them to wear the T-shirts.
Hand the “maternal” students 8 ½“ by 11” pink paper.
Hand the “paternal” students 8 ½“ by 11” blue paper.
Have one full set of “maternal” and one “paternal” students stand in the 8’ x 8’ section of
floor. There should be one “maternal chromosome 1”, one “maternal chromosome 2”,
one “paternal chromosome 1”, and one “paternal chromosome 2” in the square.
6. Explain to the class that the students represent maternal and paternal chromatin in a
diploid cell.
7. Ask the class to explain the genetic makeup of the cell.
8. Then represent the end of interphase by inviting another full set into the box. Have the
students hold hands with their twin chromosome. There should be four chromosomes two chromosome 1 and two chromosome 2.
9. Ask the class to explain what happened to the genetic makeup of the cell.
10. Have the students line up by homologous chromosomes pairs to represent the beginning
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of meiosis I.
11. The closer homologues should be asked to swap paper sheet representing crossing over.
12. Ask the class to explain what happened to the genetic makeup of each chromosome.
13. Then represent the end of meiosis I by asking the homologues to separate by moving to
opposite ends of the box.
14. Ask the class to explain what happened to the genetic makeup of offspring cells.
15. Follow this up by asking the paired chromatids to split by moving away to the front and
back sections of their side of the box explaining that gametes were formed.
16. Ask the class to explain what happened to the genetic makeup of final offspring cells.
B. “Attack of the Giant Chromosomes”
Introduction
This role playing is a fun activity to that asks students develop a play the represents the
difference between mitosis and meiosis. It particularly focuses on the separation of DNA in
mitosis and meiosis.
Materials
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8 Student volunteers
8 large swimming “pool noodles”
o Four noodles of one color
o Four noodles of another color
Paper diagram comparing mitosis and meiosis
Projected image of diagram comparing mitosis and meiosis
Sheets of paper to write a script
Procedure & Inquiry
1. Review the basic outcomes of mitosis and meiosis.
2. Call 8 students to the front of the room and instruct them to use the diagram and the
noodles to come with a demonstration that shows the difference between mitosis and
meiosis.
3. They should be given 5 minutes to plan a “play” for the rest of the class. The play should
visually demonstrate the differences in DNA distribution during mitosis and meiosis.
4. Have the students present the play to the class.
5. Ask the class to critique the series of events and provide comments about accuracy of the
“play”.
6. The class can redirect the play to demonstrate the concepts more accurately if necessary.
USEFUL INTERNET RESOURCES
1. Case studies are excellent for reinforcing scientific concepts. The University of Buffalo
produced a called The Case of the Dividing Cell: Mitosis and Meiosis in Court. It uses a
humorous scenario to reinforce the principles of cell division. This case study can be
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done in class or be given as a take-home. The case study can be found at
http://www.sciencecases.org/mitosis_meiosis/mitosis_meiosis_notes.asp.
2. Meiosis is best taught with lectures containing many visual resources. The lectures also
benefit when punctuated by brief review points between major concepts. The Biology
Project has “faculty friendly” on-line tutorials for reinforcing meiosis concept. The
website can be found at
http://www.biology.arizona.edu/cell_bio/tutorials/meiosis/page3.html.
3. Animations are a pedagogical tool known to reinforce the teaching of complex concepts
such as meiosis. This website hosted by PBS provides a useful narrated movie of
animated meiosis. This website is available at:
http://www.pbs.org/wgbh/nova/baby/divi_flash.html.
4. Human pathology is an appropriate topic for reinforcing the consequences of meiosis
errors. Down syndrome is due to abnormalities in meiosis due to a variety of factors.
Faculty can use the National Down Syndrome Society website to reinforce the principle
of nondisjunction during meiosis. The website can be found at http://www.ndss.org/.
LABORATORY IDEAS
Have students use microscope slides of fungal spores to see the outcomes of crossing
over.
a. Tell the class that they will be investigating the effects of crossing over on the properties
of fungal spores. Explain that these spores are produced by meiosis.
b. Provide students with the following materials
a. Microscope
b. Crossing over in Sordaria whole mount microscope slide
c. Sheet of paper to calculate rate of crossing over.
c. Ask students to observe the slide and identify the spores
d. Tell them to count the number of spores in each chain of spores (should be eight)
e. Have them recognize the different color spores (darker or purple, and lighter or tan)
f. Ask the students to notice and record any patterns of color distribution on each chain of
spores.
g. Ask the students to count and record the total number of darker or non-crossing over
spores per specimen on the slide.
h. Ask the students to count and record the total number of lighter or crossing over spores
per specimen on the slide.
i. Then ask the class to calculate the percent of spores that exhibit crossing over.
j. Have the students place each group of student’s data on the board to calculate the
percentage overall for the class.
k. Students can be asked to perform a Chi Square test to see if the crossing over rate for
their specimen was statistically the same as the class average.
LEARNING THROUGH SERVICE
Service learning is a strategy of teaching, learning and reflective assessment that merges the
academic curriculum with meaningful community service. As a teaching methodology, it falls
under the category of experiential education. It is a way students can carry out volunteer projects
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in the community for public agencies, nonprofit agencies, civic groups, charitable organizations,
and governmental organizations. It encourages critical thinking and reinforces many of the
concepts learned in a course.
1. Have students design high quality laminated meiosis and sexual reproduction flash cards
for use in the college library or high school study centers.
2. Have students design an educational PowerPoint presentation about meiosis for middle
school teachers.
3. Have students tutor middle school or high school biology students studying meiosis and
sexual reproduction.
4. Have students judge science fair projects related to cell division.
This project is funded by a grant awarded under the President’s Community Based Job Training Grant as implemented by the U.S.
Department of Labor’s Employment and Training Administration (CB-15-162-06-60). NCC is an equal opportunity employer and
does not discriminate on the following basis:
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against any individual in the United States, on the basis of race, color, religion, sex, national origin, age disability, political
affiliation or belief; and
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against any beneficiary of programs financially assisted under Title I of the Workforce Investment Act of 1998 (WIA), on
the basis of the beneficiary’s citizenship/status as a lawfully admitted immigrant authorized to work in the United States, or
his or her participation in any WIA Title I-financially assisted program or activity.
This workforce solution was funded by a grant awarded under the President’s CommunityBased Job Training Grants as implemented by the U.S. Department of Labor’s Employment
and Training Administration. The solution was created by the grantee and does not
necessarily reflect the official position of the U.S. Department of Labor. The Department of
Labor makes no guarantees, warranties, or assurances of any kind, express or implied, with
respect to such information, including any information on linked sites and including, but not
limited to, accuracy of the information or its completeness, timeliness, usefulness, adequacy,
continued availability, or ownership. This solution is copyrighted by the institution that
created it. Internal use by an organization and/or personal use by an individual for noncommercial purposes is permissible. All other uses require the prior authorization of the
copyright owner.
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